1. Field of the Invention
The present invention relates to an improved electromagnetic converter used for mobile communications apparatuses, and more particularly, to an electromagnetic converter having a superior anti-shock property and a vibration generating structure having a mobile electrode supported by a relatively thin spring.
2. Description of the Related Art
A typical electromagnetic sound generating body as a coil means of mobile wireless communications apparatuses, is shown in FIG. 3. That is, a magnetic pole member 2 is fixed at the center of a resin case 1 and an exciting coil 3 is arranged around the magnetic pole member 2. Also, a field magnet 4 is arranged around the exciting coil 3, and a diaphragm 6 on which an armature member 5 is fixedly installed, facing the magnetic pole member 2, is arranged at the case 1.
Recently, due to the sometimes unwanted noise produced by a sound alarming means, mobile communications apparatuses are adopting a more discrete vibratory call means.
As a vibration generating means, a flat coreless vibratory motor is used in which an eccentric weight is installed on an output shaft of a compact DC motor or an eccentric rotor is used. A motor is used because vibration of a relatively large range is possible and efficiency is improved by using a centrifugal force only.
Instead of the vibratory motor, an electromagnetic converter for obtaining both sound and vibrations, as shown in FIG. 1 of Japanese Utility Model Registration No. 2549375, has been suggested. That is, as shown in FIG. 4, a mobile magnetic pole member 22 is made by installing a magnetic pole member at the center of a spring body 7 and an exciting coil 3 is arranged around the mobile magnetic pole member 22. By applying a current having a frequency of 100 Hz, for example, vibrations are obtained so that the mobile magnetic pole member 22 is moved up and down, in the view of the drawing.
Also, since the structure in which the diaphragm 6 having the armature member installed thereon is installed at the case 1 to face the mobile magnetic member 22, is the same as the structure with the sound generating body only of FIG. 3, the same reference numerals are used and a description thereof is omitted.
In the electromagnetic converter, by applying a relatively high frequency, for example, a current having a frequency of 2-3 KHz, to the exciting coil 3, the diaphragm 6 to which the armature member 5 is fixedly installed, is vibrated to generate sound. The mobile magnetic pole member 22 cannot vibrate in a range of 2-3 KHz.
Accordingly, both functions of sound generation and vibration may be performed according to the period of the current applied to the exciting coil 3.
However, to obtain the same amount of vibration as the centrifugal force of a compact DC motor, the size of the mobile magnetic pole member 22 needs to be increased or the weight thereof needs to be increased by partially adding an auxiliary weight such as tungsten alloy. When the weight of the mobile magnetic pole member 22 is increased, if the strength of a supporting spring is not increased, when it falls, the spring body 7 is deformed so that the mobile magnetic pole member 22 cannot maintain a predetermined position. Further, when the strength of the supporting spring is increased, a large amplitude cannot be obtained without increasing the input, which is not preferred in view of efficiency.
To solve the above problems, it is an objective of the present invention to provide an electromagnetic converter providing a large vibration, which can bear an impact without increasing the strength of a supporting spring, having a simple structure, and permits increasing the weight of a mobile magnetic pole member.
Accordingly, to achieve the above objective, there is provided an electromagnetic converter having a superior anti-shock property in which a mobile magnetic pole body supported by a thin spring is driven by an exciting coil and a restricting member is arranged such that the spring is not deformed beyond a stress limit when the spring receives an impact such as precipitation.
It is preferred in the present invention that the restricting member is formed of a soft elastic member.
It is preferred in the present invention that the restricting member is arranged at a mobile side.
It is preferred in the present invention that the restricting member is arranged at a fixed side.